The persistence of foam in various aqueous industrial operations may cause process inefficiency and, in some cases, an inferior final product. The pulp and paper industry experiences some of the most troublesome foam problems. Incessant foaming commonly occurs in pulp washing, screening and bleaching processes. Foam also may surface during effluent wastewater treatment.
Entrained air tends to be a more serious type of foam. The spherical entrained air bubbles are finely dispersed in the bulk solution. Small bubble volumes tend to lack a sufficient buoyant force, and thus often become attached to nonwettable fiber parts. These fibers and fines can flocculate to the surface and form dense stable foam. As a result, the stabilized bubbles may inhibit the drainage of washing liquor through the fiber mat which in turn slows down production. Entrained air is also known to impair paper formation and tensile strength.
Surface foam, on the other hand, is a more visible problem which can be evident in wire pits, stock chests and effluent ponds. The existence of surface foam indicates an entrained air problem. On the paper machine, collapsed surface foam may be carried back through the headbox and into the sheet where holes may be formed. On the deckers, mat filtration can be reduced when surface foam is picked up by the mat. Wastewater foaming may be hazardous to both the environment as well as man.
Foam may be controlled by a variety of chemical methods. An effective antifoam should be slightly insoluble, yet dispersable, in the foaming medium. The antifoam should be able to control both entrained air and surface foam over a prolonged period of time. The present invention was developed in order to prevent or control the above described foaming problems, while avoiding the creation of any undesirable side effects in the system or on the paper machines.